Lawrence Harding "Larry" Johnston (February 11, 1918 – December 4, 2011) was an American physicist, a young contributor to the Manhattan Project. He was the only man to witness all three atomic explosions in 1945: the Trinity nuclear test in New Mexico and the atomic bombings of Hiroshima and Nagasaki in Japan. During World War II, Johnston worked at the MIT Radiation Laboratory where he invented ground-controlled approach radar. In 1944, he went to the Manhattan Project's Los Alamos Laboratory, where he co-invented the exploding-bridgewire detonator.